Thermal cracking of hydrocarbons



Nov. 20, 1962 M. B. AMls ET AL THERMAL CRACKING OF HYDROCARBONS FiledNov. 24, 1959 FRACTIONATING TOWER P H R O mm E U MW m A0 T E 8 o S 4 3 2v a 5 8 fr L M u n n 0 u n w a t u w W W S 2 2 a 3 4 v l 4 4 r G m 2h\ 2r4] :4. K 4 2 1 5 CN l 4 4 AR 4. U M 2 RF F C w m nmv m ,MIAHH N R a M wE n t w f7 lu l A Maurice Brewer Amis Attorney nice States Y 4? ace3,065,165 THERMAL CRACKING F HYDRQCARBUNS Maurice Brewer Amis and ainuelWinfield Wilson, Baton Rouge, Lac, assignors to Esso Research andEngineering Company, a corporation of Delaware Filed Nov. 24, 1959, Ser.No. 855,098 (Jlaims. (Cl. 208-48) This invention relates to hightemperature thermal noncatalytic cracking of hydrocarbons to produceolefins, diolefins and aromatic hydrocarbons, and more particularlyrelates to steam cracking in which an improved quench make-up and quenchmedium are used to quench the cracked products.

Various processes have been described in the prior art on hightemperature thermal cracking or steam cracking of hydrocarbons includinghigh boiling liquid hydrocarbons, such as residual oils and gas oils,and lower boiling hydrocarbons such as naphtha, and hydrocarbon gasessuch as ethane, propane, etc. to produce olefins such as ethylene,propylene, diolefins such as butadiene and aromatic hydrocarbons such asbenzene, toluene etc. In these high temperature cracking processes it isnecessary to quench the products from the cracking zone, that is, chillor cool them suddenly and rapidly to a lower temperature to prevent orminimize side reactions which reduce yields of desired products andincrease yields of undesired products.

In the prior art there are numerous disclosures of different quenchingagents or mediums and among these are high boiling hydrocarbons, lowerboiling hydrocarbons, water, steam etc. In many cases fouling occurs ator beyond the quench point or region and the process must be terminatedto clean the equipment. In one process of cracking kerosene or heavynaphtha a cycle oil from catalytic cracking (boiling between about 406F. and 634 F.) was considered a satisfactory quench makeup and theprocess operated for extended periods with no diiliculty in thequenching step but with some fouling. Then, at a later date it becameexpedient to feed a mixed light and heavy naphtha to the unit andshortly after this change, fouling of the equipment occurred bydeposition of tars and solids and resulted in inability to maintainsatisfactory tower top temperature due to fouling of the cooler for thereflux liquid and, of the separator tower.

The amount of naphtha mixture passing to the cracking step was reduced.The cycle oil used as a quench makeup for the heavy naphtha feed wasunsatisfactory for use in the quenching of the cracked products from themixed naphtha feed and on subsequent operations when using light naphthafeed.

Increasing the rate of quench make-up did not alleviate the problem.However, on changing the quench makeup from the light catalytic cycleoil (boiling range 400- 630 F.) to aromatic concentrate, the operatorswere able to increase the feed rate to the cracking furnaces from about10,500 b./d. to 12,500 b./d. A section of the unit was subsequently shutdown for cleaning, and, following the start-up using aromaticconcentrate for quench make-up, no further difficulty was encountered.

After much experimentation and research it was discovered thatsatisfactory quenching could be obtained by using an aromatichydrocarbon concentrate as quench makeup having a high boiling point. Asa result of continued recycling of quench oil from the separator towerto the transfer line and back to the separator tower, unsaturatedhydrocarbons formed in the cracking zone and which remain liquid in theseparator tower are polymerized to form high boiling highly condensedpitch bodies which are diflicultly soluble in the quench oil. These arethe materials which cause fouling of the separator tower,

quench oil lines, feed heat exchanger and reflux liquid cooler. Theimportant characteristics of aromatic concentrate are (1) it remains asa liquid in the separator tower and in part at the quench point orpoints and (2) it dissolves the highly condensed pitch bodies mentionedabove.

The aromatic hydrocarbon concentrate of the present invention has beenused as a quench makeup in high temperature thermal or steam crackingand has been working satisfactorily without fouling or deposition ofsolids in the separator tower, quench lines, heat exchanger or refluxliquid cooler. Improved separator tower operation and overhead producthave resulted. In addition the capacity of the cracking unit has beenincreased over that originally possible using the light catalytic cycleoil.

The aromatic hydrocarbon concentrate is an improved quench make-up whencracking mixtures of light and heavy naphthas, light naphthas alone orheavy naphthas alone to permit a greater throughput of hydrocarbon feedthan heretofore when using other quench make-up. In addition, depositionof solids as a result of coking or polymerization of the crackedproducts at the quench point or points or beyond is eliminated so thatthe cracking runs can be extended.

Another advantage results from the high boiling point of the aromaticconcentrate so that if for some reason water is present or collects inthe separator tower, as occurs in a plant start-up, the quench medium isnot lost as a result of steam distillation in the bottom of theseparator tower. This has been the case when using light catalytic cycleoil and has resulted in fouling of the quench point or points.

In the drawing the FIGURE diagrammatically shows one form of apparatusadapted for carrying out the present invention but the invention is notlimited to the exact apparatus shown as changes and modifications may bemade in the apparatus without departing from the spirit of theinvention.

Referring now to the drawing, the reference character 10 designates aline through which the hydrocarbon feed, for example, is introduced at arate of between about 10,000 and 14,000 barrels per day. The hydrocarbonmay be a light naphtha fraction or a heavy naphtha fraction or may be awide cut naphtha fraction. The naphtha feed may be a virgin feed andwhen using a light naphtha fraction the boiling point is between about60 F. and 220 F. and when using a heavy naphtha fraction the boilingrange is between about 290 F. and 440 F. The naphtha or other feed ispassed through heat exchanger 12 to preheat the naphtha feed to atemperature between about 275 F. and 305 F. and the preheatedhydrocarbon material is then passed on through line 10 into crackingfurnace or furnaces 14-. Before being introduced into the crackingfurnace the hydrocarbon feed is mixed with steam heated to a temperatureof about 340 F. and 360 F. The amount of steam used is between about 70and mol percent of the oil feed plus steam.

The cracking furnace (or furnaces) is one which contains a heating coil18 and the naphtha is heated to a high temperature in the furnacebetween about 1200 F. and 1500 F. and the time of reaction or time ofresidence of the naphtha at the high temperature is maintained from afew seconds such as two seconds to a fraction of a second as, forexample, 0.5 second depending on the temperature used, the longer timesbeing used with the lower temperatures. The pressure during cracking isbetween about 17 p.s.i.g. and 20 p.s.i.g.

The cracked products at the high temperature leave the cracking furnacethrough line 22 and are immediately quenched to a temperature of betweenabout 600 F. and

spenders 700 F. by the introduction into line 22 of a quenching mediumthrough spaced lines 24 or 26 or 2%, but preferably line 24 and thequenched mixture is introduced into the bottom portion of separatortower 30. With the present invention fouling of and coking in thetransfer outlet line 22 and in the bottom of tower 30 are prevented. Thequench lines 24, or 26 or 28 are fed from a manifold from line 27 andall the quench medium comes from line 32 controlled by valve 34. Asingle quench point is preferred although a greater number of quenchlines may be used. The quench lines 24, 2s and 23 are spacedhorizontally along the outlet transfer line 22 leading from the crackingfurnace 14 to the separator tower The quench make-up, which will bespecifically described hereinafter, forms part of the quench mediumwhich is withdrawn from the bottom of separator tower 30 along with taror bottoms and heavy oils produced in the cracking process through line38 at a temperature between about 400 F. and 450 F. and passed by pump42 through line 44 provided with a valve 45. The aromatic concentratequench make-up forms about 75 to 90% by volume of the bottoms fractionwithdrawn through line 38 which serves as a quench medium and as coolingliquid to the top of tower 30. Liquid withdrawn from the bot tom ofseparator tower 30 through lines 38 and 44 forms the quench and refluxmedium, part is passed through line 32 and to the quench lines 24, or 26or 28. A portion equivalent to the tar and heavy oil produced plusquench make-up is purged via line 63 and the rest is passed through line44 and valve 45 through the indirect heat ex- Changer 1.2 and thencethrough cooler 46 for cooling the stream to a temperature between about200 F. and 250 F. to form the reflux medium for the top of tower 30.

In passing through the heat exchanger 12, the hydro carbon feed ispreheated and the liquid reflux medium is cooled to between about 370 F.and 385 F. Before the aromatic concentrate was adopted for use as aquench make-up and as reflux for the tower 30, fouling of the heatexchanger 12 and cooler 46 occurred by the reflux liquid. Use of thearomatic concentrate eliminated this fouling of the exchanger 12 andcooler 46.

Separator tower 30 is provided with horizontally arranged verticallyspaced perforated plates 43 such as bubble tower plates, pierced plates,or the like, in the upper portion thereof to effect a roughfractionation of the cracked and quenched products and between the tarplus quench make-up and lower boiling materials. During fractionation inthe tower 30, high boiling tar plus high boiling aromatic hydrocarbonsplus quench make-up boil ing above about 400450 C. are separated andwithdrawn as part of the bottoms through line 38.

The cracked products from the furnace or furnaces 14 are introduced intothe bottom portion of the separator tower 30 below the lowermost plate48. The pressure in tower 30 is between about 14 p.s.i.g. and p.s.i.g.Also introduced into the process and into the bottom portion of theseparator tower below the lowermost plate 48 is quench make-up of thearomatic concentrate which is used in the quenching medium and thisquench make-up is introduced continuously through line 52 at a ratebetween about 400 and 800 barrels per day. Other points of in troductionmay be used.

The aromatic concentrate which is used as a quench make-up is a highboiling armoatic fraction which is extremely refractory or hard to crackso that substantially no cracking of it occurs during the quenching steand so high boiling that in and following the quenching step, a portionof the quenching medium remains liquid. The amount of quenching mediumincluding quench make-up passing through line 32 may be between about20,000 and 30,000 barrels per day when feeding between about 12,000 and14,000 barrels of oil per day (or between about 1.5 and 2.5 barrels perday of oil feed).

The ratio of quench make-up to oil feed may be between 1/17 and 1/ 35.The amount of quenching reflux pass 21. ing through line 44 and valvemay be between about. 4.3 and 5.0 barrels per day of oil feed whenfeeding about 12,000 and 14,000 barrels of oil per day (or betweenabout. 50,000 and 70,000 barrels of oil quench reflux per day). Thequenching oil remains liquid inthe bottom of the separator tower 30which is at a temperature between. about 400 and 460 F.

The aromatic concentrate of the present invention is produced bytreating a mixture of heavy catalytic cycle oil and heavy virgin gas oilwith phenol extract from the treating of a lubricating oil of a mixtureof phenol ex-- tracts from the treatment of lubricating oils. The'spentphenol or extract phase from lube oil treating was obtained by phenolextraction of lubricating oils, such as. solvent 100 neutral, solvent150 neutral, solvent 250 neutral, solvent 280 neutral and solvent 450neutral, the numher between solvent and neutral indicating the average.Saybolt Universal viscosity at 100 F. The lube oil frac tion may also beBarossa 43 (43 SSU at 210 F), Barossa- 56 (56 SSU at 210 5.) or BrightStock (SSU l60170- at 210 F.) The spent phenol or extract phase fromlube oil treating is preferred but spent phenol from other sources orfresh phenol may be used.

In one example, a heavy catalytic cycle or clarified oil. having aboiling range between about 538 F. and 1047 F. at 96% recovery was m xedwith a heavy virgin gas: oil having a boiling range between about 655 F.and. 1047 F. at 73.5% recovery and the proportions of the cycle oil(clarified oil) and virgin gas oil were in the ratio of 1.4/1 to 1/1.4.This mixture of heavy cycle oil and. heavy virgin gas oil was treatedwith a phenol extract.

Phenol extract was obtained by extracting a lubricating: oil with phenolin a liquidliquid extraction unit. Fresh.

, phenol was used in treating the lubricating oil in. a sol-- ventextraction step and following the extraction, the extract phasecontaining the phenol was separated from: the raffinate phase. Thisextract phase containing the: phenol was usedfor treating the mixture ofcatalytic cycle. oil and heavy virgin gas oil to obtain the aromatic concentrate. About 1 volume of the mixture of the catalytic. cycle oil andheavy virgin gas oil was treated with about. 1.2 to 1.4 volumes of thespent phenol or phenol extract containing about 12.5% Water and about16% oil to obtain an extract phase and a raflinate phase. The extractphase was then separated into a phenol phase and a hy'-- drocarbon phaseby distillation. The latter is called aro matic concentrate which formsthe quench make-up in the. present invention. The phenol extract fromthe lube oil extraction step will contain about 16.5 vol. percent ofthetotal oil in the feed to the heavy catalytic cycle oil-heavy virgingas oil extraction.

The aromatic concentrate prepared as above described has the followingtypical physical characteristics:

API gravity 0.5 Pour point F..- 45 Sulfur content wt. percent" 1.3Saybolt Universal viscosity at 210 F seconds 77 Aniline point F-.. 42.4Asphaltenes wt. percent 1.3 Aromatic rings do 61.0 Conradson carbonresidue do 7.4

Range, F., Boiling Points at 10 mm. Pressure F. Atmospheric PressureAbove 90% too heavy to d still Instead of using only one phenol extract,a mixture of phenol extracts may be used. For example, in somerefineries there are two lubricating phenol extraction sections, onesection being used for treating a low viscosity oil stock, such assolvent 150 neutral, and the other section being used for a highviscosity oil stock, such as solvent 450 neutral. The spent phenol orphenol extracts from the two sections are combined in about equal partsby weight prior to treating the mixture of the heavy catalytic cycle oiland the heavy virgin gas oil above referred to. The mixed phenolextracts are used in about 1.2 to 1.4 volumes to 1 volume of the mixtureof heavy cycle oil and heavy virgin gas oil just described. The extractphase was separated from the raffinate phase and the extract phase wasseparated into a phenol phase and a hydrocarbon oil phase which formsthe aromatic concentrate. The aromatic concentrate separated from theresulting phenol extract phase had about the same characteristics asthose just specifically given for a typical aromatic concentrate usefulin the present invention.

The fractionated and vaporous reaction products pass overhead from theseparator tower 30 through line 56 and are introduced into the bottom offractionating tower 62 which is provided with horizontally arranged,vertically spaced fractionating plates 64 of any conventional form. Line'56 opens into the bottom of tower 62 below the lowermost plate 64therein. Fractionated gases and vapors pass overhead from thefractionating tower 62 through line 6 and are then passed through acondenser (not shown) to separate high boiling liquids (C and heavier)including aromatic compounds such as benzene and toluene and olefius anddiolefins such as isoprene, pentene, hexene etc. from normally gaseoushydrocarbon (C and lighter) products which are further separated intodesired fractions. These recovery steps are not shown in the drawing.Fractionating tower 62 is maintained at a pressure between aboutp.s.i.g. and 12 p.S.l.g.

The bottom fraction from fractionaing tower 62 is withdrawn through line65 and returned to the bottom of the separator tower below the lowermostplate 48 therein. Other points of introduction are also satisfactory.This bottom fraction serves as additional cooling liquid for the bottomof separator tower 30. The bottom portion of fractionating tower 62 ismaintained at a temperature between about 315 F. and 320 F. The top ofthe fractionating tower 62 is maintained at a temperature between about240 F. and 270 F.

A portion of the bottoms fraction withdrawn from the separator tower 30is withdrawn from the process through valved line 68 as a purge liquid.Between about 500 and 900 barrels per day of bottoms (tars plus quenchmake-up) are withdrawn through line 60 when feeding between about 12,000and 14,000 barrels of oil per day. This purging line or withdrawing line68 removes aromatic concentrate equivalent to the addition rate but thisdoes not result in downgrading the stream withdrawn, as the streamwithdrawn from the bottom of the separator tower 30 normally goes tofuel oil or to carbon black production.

From the above description it will be seen that aromatic concentratemake-up is introduced into the bottom of separator tower 30 and thebottoms withdrawn from the tower 30 through line 38 will contain tar andthe aromatic concentrate above described. The aromaticconcentratecontaining stream withdrawn through line 38 is then usedpartly as a quenching medium by being passed through quench lines 24, or26 or 28, but preferably line 24 while another portion is passed throughline 44, valve 45, through indirect heat exchanger 12 and cooler 46. Thestream Withdrawn from the bottom of separator tower 30 through line 33is in part withdrawn through line as and discarded from the process andthis forms about 0.6% by volume of the total stream withdrawn throughline 38. About 30 to by volume of the total stream withdrawn. throughline 33 is passed through lines 44 and 32 as quench oil, and the restpassed through line 44 and valve 45 as reflux or cooling medium which isintroduced into the upper portion of the separator tower 30. The

cooled aromatic concentrate introduced through line 44 after havingpassed through the cooler 46 passes downwardly through the tower 3d andscrubs out heavy ends from the cracked and quenched vaporous and gaseousproducts passing upwardly through the separator tower 30.

The quench oil or medium containing about 90% by volume of aromaticconcentrate added through line 52 is continuously introduced into thetransfer outlet line 22 from the cracking furnace through lines 24, or26 or 2'8 so as to prevent coking of the outlet line 22 and to preventfouling of the line 22. Fouling of the bottom portion of the separatortower 30 is also prevented. The other portion of the quenching andreflux medium containing the aromatic concentrate which is passedthrough line 44 and valve 45 is passed through indirect heat exchanger12 and cooler 46 and with aromatic concentrate as quench' make-up thereis no fouling of the heat exchanger 12 and the cooler 46 or theinternals of tower 30.

in a previous operation where a light catalytic cycle oil was used asthe quenching medium, fouling of the bot tom portion of the separatortower 30 and fouling of heat exchanger 12 and cooler 46 by the refluxliquid were experienced and required shut down of the unit after a relatively short run. The unit had to be shut down even though the amount ofnaphtha feed to the contacting unit was reduced in order to continueoperation at a reduced rate of oil feed. After the process was changedto use the aromatic concentrate quench medium of the present inventionthere was no evidence of coking and fouling of the outlet line 22 fromthe furnace '14 and also there was no evidence of fouling of the bottomof the separator tower $0, the heat exchanger 12, the cooler 46 or theinternals of tower 30. In addition, the naphtha feed to the crackingfurnace 14 was increased over 1000 barrels per day over that used whenthe light cycle oil stock was used as a quenching medium.

In a specific example about 12,000 barrels per day of a mixture of 4060%of light virgin naphtha and 604070 of heavy virgin naphtha, the mixturehaving a boiling point range of between about 167 F. and 420 F., andabout 6870 mol percent of steam per day at a temperature of about 350 F.were introduced into and passed through the cracking furnace 14 under apressure of about 18 p.s.i.g. and wherein the reaction mixture wasmaintained at a temr perature of about 1300" F. for about 1 second. The

cracked products were continuously and immediately quenched by thecontinuous introduction of about 25,000 barrels per day of bottoms fromline 32 containing about 8090% by volume of the aromatic concentratequench liquid of the type above described to reduce the temper ature ofthe cracked product stream to about 640 F.

Freferahly the first quench point in the transfer line shown as quenchpoint 2 in the drawing is used. About 400-800 barrels per day of thearomatic concentrate quench make-up liquid are introduced into thebottom of the separator tower 30 through line 52. The bottoms passingthrough line 32 contains about 80-90% by volume of aromatic concentrate.

The bottom of the separator tower 30 is at about 440 F. and the bottomswithdrawn through line 38 contain about 8090 vol. percent of aromaticconcentrate quench liquid of the type above described. About 500-900barrels per day of the bottoms stream 38 is withdrawn from the processthrough line 60. About 60,000 barrels per day of the bottoms stream 33which is passed through line 44 as reflux or cooling liquid is passed tothe top of separator tower 30. The aromatic concentrate quenching andreflux liquid passing through line 44 and introduced into the top of theseparator tower 30 is at a temperature of about 220 F.

The vaporous and gaseous products passing overhead through line 56 areat a temperature of about 340-3 60 F. and contains normally gaseousunsaturated hydrocarbons, olelinic acid aromatic hydrocarbons and someheavy ends boiling in the gasoline range and some low boiling aromaticgas oil boiling to about 800 Pi. These vaporous and gaseous products arentroduced into the bottom of the fractionating tower 62 where the bottomof the tower is maintained at a temperature of about 315-330 F. and thetop of the fractionating tower 62 is maintained at a temperature ofabout 240 F. The bottoms from fractionating tower 62 are withdrawnthrough line 65 and these bottoms contain about vol. percent of materialboiling from about 200 F. to 450 F. and about 90 vol. percent boilingfrom about 450 F. to 700 F, the total stream having a gravity of about10 APE. About 2000-3 000 barrels per day of bottoms are passed throughline to the bottom of separator tower 30. The tower 62 is under apressure of about 10-12 p.s.i.g.

The vaporous and gaseous products separated in the fractionating tower62 and passing overhead through line 66 are further cooled and condensedand passed through conventional separating means to recover the usualolefins, diolefins, benzene, toluene etc. obtained in conventional steamor thermal cracking processes.

What is claimed is:

1. In a process wherein mixed naphtha feed is thermally cracked at atemperature above about 1200 F. in a cracking zone in the presence of 70to mol percent steam to produce unsaturated normally gaseoushydrocarbons and liquid aromatic, olelinic and diolefinic hydrocarbons,the improvement which comprises quenching the cracked products to atemperature below about 700 F. by injecting into the cracked productsleaving said cracking zone a quenching medium consisting essentially ofa high boiling aromatic refractory concentrate a portion of whichremains in liquid form during and after the quenching step, saidaromatic concentrate being made by treating a mixture which contains40-60% by volume of heavy catalytic cycle oil which boils above about530 F. and the rest heavy virgin gas oil which boils above about 655 F.with a phenol-containing liquid to obtain a phenol extract andrecovering the aromatic concentrate from the phenol extract phase, saidphenol-containing liquid comprising a phenol extract obtained whentreating lubricating oil in a liquid-liquid extraction step.

2. In a process wherein hydrocarbons are thermally cracked at atemperature above about 1200 F. in the presence of steam in a crackingzone to produce unsaturated normally gaseous hydrocarbons and aromatic,olefinic and diolefinic hydrocarbons and the cracked products arequenched and separated in a separating zone into a bottoms liquidfraction and a vaporous fraction and the bottoms liquid fraction is usedin part as quenching liquid and in part cooled by indirect heat exchangein a cooling zone and used as reflux liquid at the top of saidseparating zone and fouling of the quench region, the bottom of saidseparating zone and the cooling zone occurs, the improvement whichcomprises preventing fouling of the quenching region, the bottom portionof said separating zone and said cooling zone by using a quench-refluxliquid consisting essentially of a high boiling aromatic concentrateliquid which is refractory and at least in part remains liquid duringand following the quenching step and which is made by treating a mixturewhich contains 4060% by volume of heavy catalytic cycle oil which boilsabove about 530 F. and the rest heavy virgin gas oil which boils aboveabout 655 F. with a phenol-containing liquid to obtain a phenol extractand recovering the aromatic concentrate from the phenol extract phase,said phenol-containing liquid comprisng spent phenol separated from therafiinate phase in treating a lubricating oil in a liquid-liquid solventextraction step.

3-. in a process wherein hydrocarbons are thermally cracked at atemperature above about; 1200 F. in thepresence of about 70-80 molpercent steam in a cracking: zone to produce unsaturated normallygaseous hydrocar-.- hens and aromatic, olefinic and diolefinichydrocarbons and the cracked products are quenched and separated inaseparating zone into a bottoms liquid fraction and 21V v.a-.-

orous fraction and the bottoms liquid fraction is usedin '0 part asquenching liquid and in part cooled by indirect heat exchange in acooling zone and used as reflux liquld APl gravity 0.5 Pour point F.. 45Sulfur content wt. percent 1.3 Saybolt Universal viscosity at 210 Fseconds 77 Aniline point F 42.4 Asphaltenes Wt. percent 1.3 Aromaticrings do 61.0 Conradson carbon residue do 7.4

Range, F., Boiling Points at 10 mm. Pressure F. Atmospheric PressureAbove too heavy to distill 4. A process according to claim 2 wherein thequench liquid is withdrawn from the bottom portion of said separatingzone and a portion thereof discarded and make References Cited in thefile of this patent UNITED STATES PATENTS

1. IN A PROCES WHEREIN MIXED NAPHTHA FEED IS THERMALLY CRACKED AT ATEMPERATURE ABOVE ABOUT 1200*F. IN A CRACKING ZONE IN THE PRESENCE OF 70TO 80 MOL PERCENT STEAM TO PRODUCE UNSATURATED NORMALLY GASEOUSHYDROCARBONS AND LIQUID AROMATIC, OLEFINIC A ND DIOLEFINIC HYDROCARBONS,THE IMPROVEMENT WHICH COMPRISES QUENCHING THE CRACKED PRODUCTS TO ATEMPERATURE BELOW ABOUT 700*F. BY INJECTING INTO THE CRACKED PRODUCTSLEAVING SAID CRACKING ZONE A QUENCHING MEDIUM CONSISTING ESSENTIALLY OFA HIGH BOILING AROMATIC REFRACTORY CONCENTRATE A PORTION OF WHICHREMAINS IN LIQUID FORM DURING AND AFTER THE QUENCHING STEP, SAIDAROMATIC CONCENTRATE BEING MADE BY TREATING A MIXTURE WHICH CONTAINS40-60% BY VOLUME OF HEAVY CATALYTIC CYCLE OIL WHICH BOILS ABOVE ABOUT530*F. AND THE REST HEAVY VIRGIN GAS OIL WHICH BOILS ABOVE ABOUT 655*F.WITH A PHENOL-CONTAINING LIQUID TO OBTAIN A PHENOL EXTRACT ANDRECOVERING THE AROMATIC CONCENTRATED FROM THE PHENOL EXTRACT PHASE, SAIDPHENOL-CONTAINING LIQUID COMPRISING A PHENOL EXTRACT OBTAINED WHENTREATING LUBRICATING OIL IN A LIQUID-LIQUID EXTRACTION STEP.